Sound absorbing body, sound absorbing plate, and sound absorbing unit

ABSTRACT

To provide a sound absorbing structure having a superior sound absorbing characteristic and an external appearance of the sound absorbing structure which does not cause flicker or the like, by disposal, for example, in the front of an air chamber, a plurality of ribs (2a) are disposed on one surface of the sound absorbing board body (2), and a plurality of through-holes (3) are provided in basal portions (2b) between the ribs (2a) to form a porous structure. Concealing materials (5) are provided between the ribs (2a) of the sound absorbing board body to conceal the through-holes (3), respectively.

TECHNICAL FIELD

The present invention relates to a sound absorbing body, sound absorbingboard, and sound absorbing unit disposed on a surface of a soundabsorbing structure in the use of sound-proof walls, tunnel interiorwalls, and so on in the field of indoor acoustic design for ceilings andwall surfaces and in the field of outdoor noise control.

BACKGROUND ART

Heretofore, fiber mat boards such as asbestos boards, glass wool boards,etc. are used as sound absorbing boards provided on ceilings, wallsurfaces, and so on. These fiber mat boards have a disadvantage thatthese boards are inferior in sound absorbing property in a low frequencyband, while they have a sound absorbing effect in middle and high tonebands.

Therefore, an arrangement of a sound absorbing board in which a porousstructure of a flat board with a large number of through-holes formedtherein is provided in the front of an air chamber is known as a soundabsorbing structure excellent in sound absorbing property in a lowfrequency band.

However, the conventional porous structure sound absorbing board has aproblem as follows. Since the board has a shape in which a large numberof holes which open in a plane are formed, these holes are visible fromthe outside when the board is disposed to a ceiling or wall surface sothat a visual point of a person cannot come on a wall surface and anunpleasant feeling is given to the person by flicker. Furthermore, thereis a limitation in design because the structure has such a simple shapein which only a large number of holes are formed to open in a plane.Furthermore, there is another problem that the large number of holes arestained to make the external appearance poor or to make the soundabsorbing property deteriorate.

The present invention has an object to provide a sound absorbing bodyhaving a porous structure which is disposed in the front of an airchamber so as to form a sound absorbing structure with a good soundabsorbing property, and which can provide a good external appearancewithout causing visual flicker.

Another object of the present invention is to provide a sound absorbingboard in which while a porous structure is provided with a large numberof through-holes, those holes can be prevented from being stained orchoked.

DISCLOSURE OF THE INVENTION

The above-mentioned object of the present invention can be achieved by asound absorbing body comprising:

a sound absorbing main body formed almost in the shape of a plate;

a plurality of ribs formed convexly at predetermined intervals on afront surface of the sound absorbing main body for reinforcing the soundabsorbing main body, each of the ribs having a desired cross-sectionalshape;

through-holes formed through the sound absorbing main body from itsfront surface to its back surface correspondingly to the respectiveribs; and

concealing materials disposed between the ribs on the front surface ofthe sound absorbing main body for concealing the through-holes.

It is preferable to make the ribs integrally with the sound absorbingmain body.

Further, the above-mentioned object of the present invention can beachieved by a sound absorbing board comprising:

a sound absorbing board body formed almost into a substantially flatplate;

a plurality of rigs provided on a front surface of the sound absorbingmain body for reinforcing the sound absorbing main body;

a plurality of through-holes disposed at a base portion between the ribsprovided on the sound absorbing main body; and

concealing materials disposed on the front surface of the soundabsorbing main body for concealing the through-holes.

It is preferable to make the height of the upper surface of theconcealing materials not higher than the height of the upper surface ofthe ribs respectively.

The above-mentioned object of the present invention can be achieved by asound absorbing board characterized by comprising:

a sound absorbing board body formed into a substantially flat plate;

a plurality of ribs provided on a front surface of the sound absorbingboard body for reinforcing the sound absorbing main body, each of theribs having a cross-sectional shape widened toward its top end; and

a plurality of through-holes formed through the sound absorbing boardbody to reach its back surface in portions at root ends of the ribsconcealed by the top ends of the ribs;

wherein each of the through-holes has a diameter which is longer thanwidth of the root end of each of the ribs and shorter than width of thetop end of each of the ribs so that the through-holes open on both sidesof each of the ribs.

Further, the above-mentioned object of the present invention can beachieved by a sound absorbing body disposed in the front of an airchamber so as to constitute a sound absorbing structure together withthe air chamber characterized by comprising:

a plurality of ribs formed convexly at predetermined intervals on anopposite side to the air chamber so as to form a resonant space whichcommunicates with the air chamber and has a closed upper face to therebyprovide a sound absorbing effect due to a resonant effect; and

a plurality of through-holes provided in at least one of base portionson a side surface of the respective ribs and on a root portion betweenthe ribs so that the through-holes communicate with the air chamber.

It is preferable to provide sound absorbing material at least on inneror outer surface of the basal portions formed between the ribs.

It is preferable to provide partition walls which are disposed at leaston the rear surfaces of the ribs or on the basal portions in order topartition the air chamber located in the back.

It is preferable that each of the ribs has a portion with its sectionalshape widened toward the front end.

It is preferable that the volumes of the resonant spaces defined by theribs are classified into at least two groups.

The above objects can be achieved by a sound absorbing unitcharacterized by comprising a sound absorbing body as described hereinand a back board integrally provided with the sound absorbing body anddisposed in the back of the sound absorbing body at a distance so as todefine an air chamber therebetween.

(OPERATION)

In the sound absorbing body according to the present invention, aplurality of ribs each having a desired cross-sectional shape are formedconvexly at predetermined intervals on a front surface of the soundabsorbing main body for reinforcing the sound absorbing main body.Further, through-holes are formed through the sound absorbing main bodyfrom its front surface to its back surface correspondingly to therespective ribs. Furthermore, concealing materials are provided betweenthe ribs on the front surface of the sound absorbing board main body forconcealing the through-holes.

In the sound absorbing body of an embodiment according to the presentinvention, a plurality of ribs each having a desired cross-sectionalshape are formed integrally with the sound absorbing main body andconvexly at predetermined intervals on a front surface of the soundabsorbing main body for reinforcing the sound absorbing main body.Further, through-holes are formed through the sound absorbing main bodyfrom its front surface to its back surface correspondingly to therespective ribs. Furthermore, concealing materials are provided betweenthe ribs on the front surface of the sound absorbing main body forconcealing the through-holes.

In the sound absorbing board according to another embodiment of thepresent invention, a plurality of ribs are formed on a front surface ofthe sound absorbing board main body for reinforcing the sound absorbingmain body. Accordingly, for example, when such a sound absorbing boardis attached in the front of an air chamber so as to constitute a soundabsorbing structure, if the sound absorbing board main body is attachedwith its surface on which the ribs are formed outside, an appearance inwhich a number of ribs are arranged side-by-side is provided. Further,concealing materials are provided between the ribs on the front surfaceof the sound absorbing board main body for concealing the through-holes.Accordingly, no unpleasant feeling given to a person even though thelarge number of holes are formed. Further, because the sound absorbingboard has a porous structure in which a large number of through-holesare provided, a sound absorbing structure good in sound absorbingproperty in a low frequency band can be formed by a combination of theporous structure and the air chamber. Further, various externalappearances can be provided by appropriately changing the intervalsbetween the ribs and the width of the ribs, so that the design can bechanged variously. Further, the plurality of ribs have a reinforcingfunction, so that the strength of the sound absorbing board can beimproved.

Since the concealing materials for concealing the through-holes areprovided on the surface on the side on which the ribs are provided inthe sound absorbing board main body, the through-holes cannot be seenfrom the outside and flicker caused by the large number of holes can beprevented greatly so that a good external appearance can be provided.Further, the concealing materials can protect the through-holes toprevent stain or dust from being deposited thereinto, so that thethrough-holes can be prevented from being choked over a long term.

In the sound absorbing board according to an embodiment of the presentinvention, the configuration is such that the ribs and the concealingmaterials are made even in their upper surface or the upper surface ofthe ribs project beyond the upper surface of the concealing materialsbecause the height of the upper surface of the concealing materials ismade to be not higher than the upper surface of the ribs.

In the sound absorbing board according to another embodiment of thepresent invention, a plurality of ribs each having a cross-sectionalshape widened toward its top end are provided on a front surface of thesound absorbing board body for reinforcing the sound absorbing boardbody, and the board body has a porous structure in which a plurality ofthrough-holes are formed through the sound absorbing board main body toreach its back surface in portions at root ends of the ribs concealed bythe top ends of the ribs. Each rib has a cross-sectional shape widenedtoward its top end, for example, like a reversed trapezoid and thediameter of each through-hole is set to be longer than the width of theroot end of the rib and shorter than the width of the top end of the ribso that the through-holes open on both sides of each of the ribs.Accordingly, for example, by attaching the sound absorbing board infront of the air chamber, it is possible to constitute a sound absorbingstructure which is superior in sound absorbing characteristic especiallyin the low frequency area, and by disposing the sound absorbing board inthe state that the surface of the sound absorbing board on which theribs are formed is disposed outside the sound absorbing structure, it ispossible to obtain a preferable appearance. Further, the plurality ofthrough-holes communicating with the other surface of the soundabsorbing board main body are formed through the sound absorbing boardbody in portions at root ends of the ribs concealed by the top ends ofthe ribs. Accordingly, the through-holes are not clearly seen from theoutside so that no visual flickering or the like is caused by a numberof through-holes and therefore no unpleasant feeling is caused by theflickering.

In the sound absorbing body according to the present invention, when thesound absorbing body is attached to the front of the air chamber tothereby constitute a sound absorbing structure, the plurality of ribsthe upper surface of which is blocked become the front surface tothereby obtain an external appearance in which the large number of ribsare disposed. Because the through-holes are formed in side surfaces ofthe ribs or in the basal portions between the ribs, the through-holesare inconspicuous. Accordingly, there is no flicker caused by thethrough-holes so that no unpleasant feeling is given to a person.

Further, because the sound absorbing body has a porous structure inwhich a large number of through-holes are provided, a sound absorbingstructure good in sound absorbing property in a low frequency band canbe formed by a combination of the sound absorbing body and the airchamber. Furthermore, because spaces among the ribs serve as resonantspaces in this occasion, not only the sound absorbing property isimproved but also the sound absorbing structure can be made thincompared with the case where the conventional porous board is used.

Furthermore, because various external appearances can be provided bychanging the interval and width of the ribs suitably, the design can bechanged variously. Further, because the plurality of ribs also have areinforcing effect, the strength of the sound absorbing body can beimproved.

In a sound absorbing body of the present invention, the aforementionedsound absorbing body further comprises a sound absorbing material whichis disposed at least on inner or outer surface of the basal portionsbetween the ribs, by which not only the resonant frequency band can bewidened but also the sound absorbing property in a wide frequency bandcan be improved.

In a sound absorbing material of the present invention, the soundabsorbing body further comprises partition walls which are disposed atleast on the rear surfaces of the ribs or on the basal portions in orderto partition the spaces in the ribs and the air chamber located in theback. Accordingly, a plurality of independent small chambers are formedso that resonant frequencies corresponding to the independent smallchambers can be provided, or in other words, a sound absorbing structurehaving a desired sound absorbing property can be designed easily if thevolumes of the independent small chambers are designed to be in valuescorresponding to required resonant frequencies.

Further, in a sound absorbing body of the present invention, each of theribs has a portion with its sectional shape widened toward the frontend. Accordingly, the effect in which the ribs conceal the through-holesis high, so that a good external appearance is obtained. At the sametime, there arises an effect that stain or dust is prevented from beingdeposited into the through-holes, so that the through-holes can beprevented from being choked for a long term.

In a sound absorbing body of the present invention, the sizes of theribs are classified into two or more kinds so that the volumes of theresonant spaces defined by the plurality of ribs are classified into atleast two groups. Accordingly, a plurality of resonant frequencies canbe provided, so that the sound absorbing property in a wide frequencyband can be improved.

In a sound absorbing body of the present invention, a sound absorbingunit comprises the sound absorbing body as mentioned above; and a backboard integrally provided with the sound absorbing body and disposed inthe back of the sound absorbing body at a distance so as to define anair chamber therebetween. Accordingly, a wall surface having a requiredsound absorbing property can be formed simply by arranging such soundabsorbing units, so that a sound absorbing structure can be producedeasily on site. In the sound absorbing board and the sound absorbingbody according to embodiments of the present invention respectively, theconfiguration is such that the ribs and the concealing materials aremade even in their upper surface or the upper surface of the ribsproject beyond the upper surface of the concealing materials because theheight of the upper surface of the concealing materials is made to benot higher than the upper surface of the ribs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of a sound absorbing boardaccording to an embodiment of the present invention.

FIG. 2 is a schematic sectional view taken along line 2--2 of FIG. 1showing the sound absorbing board depicted in FIG. 1.

FIG. 3 is a schematic sectional view showing an example of soundabsorbing structure configured by using the sound absorbing boarddepicted in FIG. 1.

FIGS. 4(a), 4(b) and 4(c) are schematic sectional views showing soundabsorbing boards using concealing materials in different shapesrespectively.

FIGS. 5(a), 5(b), 5(c) and 5(d) are schematic sectional views showingsound absorbing boards using concealing materials in different shapesrespectively.

FIG. 6 is a schematic perspective view showing a sound absorbing boardaccording to another embodiment of the present invention.

FIG. 7 is a schematic perspective view showing a sound absorbing boardaccording to a further embodiment of the present invention.

FIG. 8 is a schematic sectional view taken along line 8--8 of FIG. 7showing the sound absorbing board depicted in FIG. 7.

FIG. 9 is a bottom view of the sound absorbing board depicted in FIG. 7.

FIG. 10 is a schematic perspective view showing a sound absorbing boardaccording to another embodiment of the present invention.

FIG. 11 is a schematic sectional view taken along line 11--11 of FIG. 10showing the sound absorbing board depicted in FIG. 10.

FIGS. 12(a), 12(b), 12(c) and 12(d) are schematic sectional viewsrespectively showing sound absorbing structures subjected to measurementof the sound absorbing property.

FIG. 13 is a graph showing the results of measurement of the soundabsorbing property in the sound absorbing structures in which a soundabsorbing board made from asbestos is used.

FIG. 14 is a graph showing the results of measurement of the soundabsorbing property in the sound absorbing structures in which a soundabsorbing board made from wood is used.

FIG. 15 is a schematic perspective view of a sound absorbing structureconfigured by using a sound absorbing body according to an embodiment ofthe present invention.

FIG. 16 is a schematic sectional view of the sound absorbing structure.

FIGS. 17(a) and 17(b) are schematic sectional views showing embodimentsin which through-holes are provided in positions different from those inthe aforementioned embodiment.

FIGS. 18(a) to 18(g) are schematic sectional views showing embodimentsof the sound absorbing body having a different section.

FIGS. 19(a) and 19(b) are schematic sectional views showing embodimentsof the sound absorbing body having a section different from that in theaforementioned embodiment.

FIG. 20 is a schematic sectional view showing a sound absorbing bodyaccording to another embodiment of the present invention.

FIG. 21 is a schematic sectional view showing a sound absorbing unitaccording to a further embodiment of the present invention.

FIGS. 22(a) and 22(b) are schematic sectional views of the soundabsorbing unit according to further embodiments of the presentinvention.

FIGS. 23(a), 23(b) and 23(c) are schematic sectional views of the soundabsorbing body according to further embodiments of the presentinvention.

FIGS. 24(a) to 24(h) are schematic sectional views showing sectionalstructures in Examples 5 to 12.

FIGS. 25(a) to 25(c) are schematic sectional views showing sectionalstructures in Comparative Examples 4 to 6.

FIG. 26 is a graph showing the sound absorbing property in Examples 5,6, 7, 9, and 10.

FIG. 27 is a graph showing the sound absorbing property in Examples 7,8, 9, and 10.

FIG. 28 is a graph showing the sound absorbing property in Examples 11and 12.

BEST MODE OF THE PRESENT INVENTION

The present invention will be described in more detail with reference tothe accompanying drawings.

FIG. 1 is a schematic perspective view of a sound absorbing boardaccording to an embodiment of the present invention, and FIG. 2 is aschematic sectional view of the sound absorbing board taken along lineA--A of FIG. 1.

The sound absorbing board designated as a whole by reference numeral 1has a sound absorbing board body 2 which is a substantially flatplate-like member as a whole. This sound absorbing main body 2 has aplurality of ribs 2a provided in parallel to each other on one of thesurfaces of the board and has a porous structure in which a plurality ofthrough-holes 3 are provided in basal portions 2b between the ribs 2a.The sound absorbing board 1 further has concealing materials 5 which areprovided between the ribs 2a so as to conceal the through-holes 3respectively. Each of the concealing materials 5 has a long concealingportion 5a on the front surface side, and a leg portion 5b forconnecting the concealing portion 5a to the basal portion 2b at aposition in which there is no through-hole 3 provided.

FIG. 3 is a schematic sectional view showing an example of the soundabsorbing structure constituted by using this sound absorbing board 1.In FIG. 3, the reference numeral 7 designates a wall surface to whichthis sound absorbing structure is attached; 8, an air chamber; and 9, asound absorbing material such as glass wool disposed in the front of theair chamber 8. The sound absorbing board 1 is disposed in front of thesound absorbing material 9 so that the ribs 2a face on the outside.Accordingly, the sound absorbing board 1 is disposed as the frontmostsurface of the sound absorbing structure, so that the rib 2a sidesurface is in a visible state. Incidentally, as the sound absorbingmaterial 9, there may be used not only glass wool but also porousmaterials such as rock wool, fiber mat material, or the like, filmmaterials such as sail cloth, or the like, and so on.

In the sound absorbing structure configured as described above, thelarge number of through-holes 3 are not visible even though the largenumber of through-holes 3 are formed in the surface of the board sincethe surface on which the ribs 2a and concealing materials 5 of the soundabsorbing board 1 are disposed, forms an external appearance.Accordingly, there is no flicker caused by the through-holes 3, so thatthere is formed a stripe-like good external appearance which is suchthat the ribs 2 and the concealing materials 5 are disposed.Accordingly, not an unpleasant feeling but a good impression can begiven to a person who sees the sound absorbing board. Further, becausethe plurality of ribs 2a have a reinforcing effect, the strength of thissound absorbing board is higher than that of the simply flat plate-likesound absorbing board. Accordingly, support members (not shown) forattaching the sound absorbing board 1 to the wall 7 at an intervaltherebetween to form an air chamber 8 can be simplified. Furthermore,because the concealing materials 5 can prevent stain or dust from beingdeposited in the through-holes 3, the through-holes 3 can be preventedfrom being choked over a long term.

In the sound absorbing structure shown in FIG. 3, a sound wave from theoutside collides with the sound absorbing board 2 located in the frontside and passes through the through-holes 3 into the sound absorbingmaterial 9 and the air chamber 8 located in the back side, so that thesound absorbing material 9 and the air chamber 8 absorb the sound waveby the isothermal change or adiabatic change due to heat transmission.In this occasion, a sound absorbing effect mainly in a low frequencyband is obtained by using the through-holes 3 and the air chamber 8 incombination whereas a sound absorbing effect in a middle or high toneband is obtained by the sound absorbing material 9. In this manner, thissound absorbing structure has a sound absorbing effect excellent in arange of from a low frequency band to a high frequency band.

In the sound absorbing board 1 of the aforementioned embodiment, thelarge number of through-holes 3 formed in the sound absorbing board body2 are provided to make entrance of sound into the air chamber 8 easy.The numerical aperture, hole diameter, pitch, etc. of the through-holes3 may be determined taking into account the sound-absorption frequencyproperty based on a combination of the through-holes 3 and the airchamber. Generally, the numerical aperture is preferably in a range offrom about 2 to about 20%, more preferably in a range of from about 5 toabout 10%. Further, the hole diameter is preferably in a range of about3 to 15 mm, more preferably in a range of from about 5 to about 7 mm.Further, the hole pitch may be determined suitably correspondingly tothe aforementioned numerical aperture and hole diameter ranges.

The width and interval of the ribs 2a formed on the sound absorbingboard body 2 may be determined taking into account the aforementionedhole pitch of the through-holes 3 so that a good external appearance isprovided. Further, the height of the ribs 2a may be determined takinginto account the reinforcing effect of the ribs 2a and the height of theconcealing materials 5. Generally, the height of the ribs 2a isdetermined to be preferably in a range of from about 0.5 times to about2 times, more preferably about 1 time as much as the thickness of thebasal portions 2b. Not only the trapezoidal shape having a wide bottomportion in the embodiment shown in the drawings but also a rectangularor reverse-trapezoidal shape, or the like, may be used as the sectionalshape of the ribs 2a. These shapes can be changed suitably to obtain agood external appearance.

The concealing materials 5 are provided to conceal the large number ofthrough-holes 3. Generally, the width of the concealing materials 5 isselected to be larger than the hole diameter of the through-holes 3.Incidentally, the sectional shape, size, etc. of the concealingmaterials 5 are not limited to the embodiment shown in the drawings, andvarious changes may be made if entrance of sound wave into thethrough-holes 3 is not blocked.

For example, FIG. 4 shows examples of a sectionally T-shaped concealingmaterial. FIG. 4(a) shows a concealing material 5A which is formed so asto be lower than the rib 2a. FIG. 4(b) shows a concealing material 5Bwhich is formed so as to be higher than the rib 2a. FIG. 4(c) shows aconcealing material 5C which is formed so as to be higher than the rib2a and wider than the groove width between ribs 2a and 2a.

Further, FIG. 5 shows examples of the concealing material different insectional shape. FIG. 5(a) shows a concealing material 5D which has asectionally semicircular concealing portion. FIG. 5(b) shows aconcealing material 5E which has a sectionally triangular concealingportion. FIG. 5(c) shows a concealing material 5F which has asectionally arc-like concealing portion. FIG. 5(d) shows a concealingmaterial 5G which has a sectionally circular concealing portion.

As described above, although the concealing materials 5 (and 5A to 5G,etc.) are provided to conceal the through-holes 3, they are provided sothat entrance of sound wave into the through-holes 3 is not blocked.Therefore, the sectional area of a passage formed between the concealingmaterial 5 and the sound absorbing board body 2 is generally selected tobe larger than the sectional area of the through-hole 3.

If the sectional area is selected as described above, the numericalaperture of the sound absorbing board 1 is determined on the basis ofthe numerical aperture of the through-hole 3, so that the provision ofthe concealing materials 5 has little influence on the sound absorbingproperty. Accordingly, not only the sound absorbing property of thesound absorbing board can be determined correspondingly to the design ofthe through-holes 3 (the design concerning numerical aperture, holediameter, hole pitch, etc.) but also the shape, size, etc. of theconcealing materials 5 can be desirably determined taking into accountthe external appearance, so that the design can be changed as desired.

Alternatively, the sectional area of the through-holes of the passageformed between the concealing material 5 and the sound absorbing boardbody 2 may be selected to be smaller than the sectional area of thethrough-hole so that the numerical aperture of the sound absorbing board1 can be determined on the basis of the passage formed between theconcealing material 5 and the sound absorbing board body 2. In thisconfiguration, the sound absorbing property can be changedcorrespondingly to the concealing material 5.

The material for the sound absorbing board body 2 of the sound absorbingboard 1 is not limited specifically. For example, a material havinglittle sound absorbing effect in itself, such as wood, plastics, etc.,may be used, or a fiber mat-like material having a sound absorbingeffect, such as asbestos, glass wool, etc., may be used. Further, thesame material as that for the sound absorbing board body 2 can be usedas the material for the concealing material 5. The sound absorbing boardbody 2 and the concealing material 5 may be formed from one and the samematerial or from different materials. Incidentally, when a materialhaving a sound absorbing effect is used as the material for the soundabsorbing board body 2 and/or concealing material 5, there is obtainedan advantage that the sound absorbing effect is improved more greatly.

Although the aforementioned embodiment has shown the case where theconcealing materials 5 are disposed for concealing the through-holes 3formed between the ribs 2a, 2a, the concealing materials 5 can beomitted.

FIG. 6 shows an embodiment in this case. In FIG. 6, a large number ofthrough-holes 3 are formed in basal portions 2b between ribs 2a, 2a ofthe sound absorbing board body 2 so as not to be concealed. In thisembodiment, the through-holes 3 located in bottom portions of groovesformed between the ribs 2a, 2a are visible but not so conspicuousbecause the ribs 2a are provided so as to be emphasized. Accordingly,there is no flicker caused by the large number of holes, so that nounpleasant feeling is given.

FIGS. 7 to 9 show a further embodiment of the present invention.

In this embodiment, a sound absorbing board 11 is substantiallyconstituted by only a flat-plate-like sound absorbing board body 12 as awhole. This sound absorbing board body 12 has a plurality of ribs 12adisposed in parallel to each other on one surface of the sound absorbingboard body 12, and a plurality of holes 13 formed in basal portions ofthe ribs 12a. Each of the ribs 12a has a cross-sectional shape widenedtoward its top end like a reversed trapezoid as shown in FIG. 7. Each ofthe holes 13 has a diameter which is smaller than the width of the frontend of the rib 12a but larger than the width of the bottom portion ofthe rib 12a. Accordingly, the upper end of the hole 13 is opened in aportion which is a portion of intersection between the rib 12a and thebasal portion 12b and which is a portion concealed by the front end ofthe rib 12a, so that there is formed a through-hole which pierces thesound absorbing board body 12 from one side to the other side. Here, thearea of the hole 13 opened in the portion of intersection between therib 12a and the basal portion 12b is determined to obtain a numeralaperture required for a desired sound absorbing property.

Incidentally, the hole 13 is not limited to the case of a hole having alarge diameter so as to be opened on opposite sides of one rib 12a asshown in the drawings. A hole having a small diameter may be used so asto be opened on only one side of the rib 12a. In this case, the holehaving a small diameter may be disposed only in one side of or in eachof the opposite sides of the rib 12a.

The sound absorbing board 11 of this embodiment can be also used insteadof the sound absorbing board 1 in the sound absorbing structureconfigured as shown in FIG. 3, so that a sound absorbing structure goodin sound absorbing property in a low frequency band can be formed. Inthis occasion, by disposing the ribs 12a on the outer surface side, agood groove-like external appearance formed from the parallel ribs canbe provided so that the holes 13 are invisible from the outside.

Although the above embodiments have shown the case where ribs 2a, 12aare disposed so as to extend in only one direction, ribs extending in adirection perpendicular to the ribs 2a, 12a may be further provided atintervals of a suitable distance. Although the above embodiments haveshown the case where ribs 2a, 12a are disposed on only one surface sothat the other surface is flat, the other surface is not limited to sucha flat surface. For example, ribs may be formed on the other surface. Inthis case, the sectional shape, direction, etc. of ribs may be selectedto be the same as those of the ribs 2a, 12a formed on one surface or tobe different from those of the ribs 2a, 12a.

Next, FIGS. 10 and 11 show a further embodiment of the presentinvention.

In this embodiment, a sound absorbing board 21 has a simpleflat-plate-like sound absorbing board body 22 without any rib, andthrough-holes 23 which are formed in the sound absorbing board body soas to be disposed as a plurality of rows. Further, a plurality ofconcealing materials 25 are attached to one surface of the soundabsorbing board body 22 so that the rows of through-holes 23 areconcealed by the concealing materials 25, respectively.

Similarly to the sound absorbing boards of the other embodiments, thesound absorbing board 21 of this embodiment can be also used instead ofthe sound absorbing board 1 in the sound absorbing structure configuredas shown in FIG. 3, so that a sound absorbing structure good in soundabsorbing property in a low frequency band can be formed. In thisoccasion, by arranging the concealing materials 25 on the outer surfaceside, it is possible to obtain a groove-like external appearance whichis formed from the parallel concealing materials 25 so that thethrough-holes 23 are not visible from the outside. Incidentally,modifications may be made such that concealing materials or ribs aredisposed on a surface opposite to the surface of the sound absorbingboard body 22 on which the concealing materials 25 or ribs are disposed.

The materials for forming the sound absorbing board body and concealingmaterials, the numerical aperture of the through-holes, and so on, inthe embodiments shown in FIGS. 6 to 11 are the same as those in thedescription of the embodiments shown in FIGS. 1 to 5.

The results of measurement of the sound absorbing property are shown asfollows.

EXAMPLE 1!

As shown in FIG. 12(a), a sound absorbing structure (Structure A) wasproduced so that a sound absorbing material 9 and a sound absorbingboard 1 were disposed in the front of an air chamber 8. The soundabsorbing board 1 used herein was constituted by a sound absorbing boardbody 2 with ribs 2a, and concealing materials 5. The size of eachportion was as shown in the drawing (unit: mm). The material for thesound absorbing board body 2 was an asbestos board (density: 37 kg/m³).The material for the concealing materials 5 was wood. The hole diameterof the through-holes 3 was 7 mm. The hole pitch in the direction alongthe ribs 2a was 22 mm. Further, the sound absorbing material 9 wasformed from glass wool (density: 32 kg/M³).

EXAMPLE 2!

As shown in FIG. 12(b), a sound absorbing board body 2 which was thesame as that in Example 1 was singly used as the sound absorbing boardto thereby produce a sound absorbing structure (Structure B) which wasthe same as that in Example 1. The size of each portion and the materialfor each portion were the same as those in Example 1.

Comparative Example 1!

As shown in FIG. 12(c), a sound absorbing structure (Structure C) wasproduced from only a sound absorbing board 30 with no through-hole. Thesize of the sound absorbing board 30 and the material therefor were thesame as those of the sound absorbing board body 2 in Example 1, exceptthat the board 30 had no through-hole.

EXAMPLE 3!

The same structure (that is, Structure A shown in FIG. 12(a)) and thesame size as those in Example 1 were used but wood was selected to bethe materials for the sound absorbing board body 2 and the concealingmaterials 5.

EXAMPLE 4!

The same structure (that is, Structure B shown in FIG. 12(b)) and thesame size as those in Example 2 were used but wood was selected to bethe material for the sound absorbing board body 2.

Comparative Example 2!

The same structure (that is, Structure C shown in FIG. 12(c)) and thesame size as those in Comparative Example 1 were used but wood wasselected to be the material.

Comparative Example 3!

As shown in FIG. 12(d), there was produced a sound absorbing structure(Structure D) which was the same as that in Example 1, except that asound absorbing board 32 obtained by forming a large number ofthrough-holes 33 in a flat board was used. Wood was selected to be thematerial for the sound absorbing board 32, and the thickness thereof wasselected to be 9 mm. The hole diameter of the through-holes 33 wasselected to be 7 mm. The pitch of the through-holes 33 was selected tobe 22 mm both in a lateral direction and in a direction perpendicularthereto.

Upon the above Examples 1 to 4 and Comparative Examples 1 to 3, thevertical incidence sound absorbing rate was measured. The results of themeasurement are shown in Tables 1 and 2. FIGS. 13 and 14 show the graphsillustrated from the results.

                  TABLE 1                                                         ______________________________________                                        Frequency                                                                     (Hz)     200    250    315  400  500  630  800  1000                          ______________________________________                                        Example 1                                                                              98.2   96.5   88.3 75.0 65.9 61.5 66.8 72.1                          Example 2                                                                              97.4   98.7   92.2 79.4 67.7 62.0 70.8 77.3                          Com. Ex. 1                                                                             42.6   34.0   42.2 40.4 33.7 34.8 37.0 38.3                          ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Frequency                                                                     (Hz)     200    250    315  400  500  630  800  1000                          ______________________________________                                        Example 3                                                                              95.8   95.0   70.4 60.3 65.5 42.6 42.0 51.5                          Example 4                                                                              95.3   98.0   77.3 65.9 54.0 46.5 44.0 58.9                          Com. Ex. 2                                                                             35.0   24.0   22.3 20.0 23.5 14.5 11.9 10.0                          Com. Ex. 3                                                                             93.5   94.8   73.9 57.2 55.5 44.9 38.3 51.3                          ______________________________________                                    

It is apparent from Tables 1 and 2 and FIGS. 13 and 14 that the soundabsorbing rate of the sound absorbing boards (Comparative Examples 1 and2) without any through-hole is low whereas the sound absorbing rate ofthe sound absorbing boards each having a porous structure obtained byforming through-holes in a sound absorbing board is improved greatly,particularly, the sound absorbing property in a low frequency band isimproved.

In this occasion, if the same material is used for the sound absorbingboard, the sound absorbing property in the case (Examples 2 and 4) whereribs are provided on the sound absorbing board, the sound absorbingproperty in the case (Examples 1 and 3) where ribs and concealingmaterials are provided and the sound absorbing property in the case(Comparative Example 3) where a flat porous sound absorbing board 32 isused are nearly equal to each other. This fact shows that the soundabsorbing property is not deteriorated regardless of the provision ofribs and regardless of the provision of concealing materials.Accordingly, the present invention can improve the external appearancewhile ribs and concealing materials are provided without anydeterioration in sound absorbing property.

Further, it has been found that the sound absorbing property in the case(Examples 1 and 2) where a material having a sound absorbing effect initself is used for the sound absorbing board is better than that in thecase (Examples 3 and 4) where wood having a small sound absorbing effectis used.

FIG. 15 is a schematic perspective view of a sound absorbing structureconfigured by using a sound absorbing body according to an embodiment ofthe present invention, and FIG. 16 is a schematic sectional view of thesound absorbing structure of FIG. 15.

In the drawings, the reference numeral 101 designates a wall surface;102, an air chamber; and 103, a sound absorbing body which is attachedto the wall surface 101 through spacers 104 so as to be located in thefront of the air chamber 102. The wall surface 101, the air chamber 102and the sound absorbing body 103 constitute a sound absorbing structure.The sound absorbing body 103 is formed from a board material of metal,plastics, wood, or the like, and has: a plurality of ribs 106 providedso as to project to a side opposite to the air chamber 102 and formresonant spaces 105 communicated with the air chamber 102; basalportions 107 formed between the ribs 106; and a plurality ofthrough-holes 108 formed in the basal portions 107 so as to becommunicated with the air chamber 102.

In this sound absorbing structure, a sound wave from the outsidecollides with the sound absorbing body 103 as a surface and enters intothe air chamber 102 in the back thereof and into the resonant spaces 105in the ribs 106 through the through-holes 108, so that the sound wave isabsorbed by the resonant effect of the air chamber 102 and the resonantspaces 105. In this occasion, this sound absorbing structure hascharacteristic in which the sound absorbing effect is particularly highin a low frequency band, as is obvious from results of sound absorbingexperiments upon Examples (1) through (8) which will be described later.Further, the sound absorbing effect in this sound absorbing structure inwhich resonant spaces 105 are provided in the ribs 106 is higher thanthat in the conventional sound absorbing structure in which a porousboard is merely disposed in the front of the air chamber. Accordingly,this sound absorbing structure also has characteristic in which thethickness of the sound absorbing structure can be reduced remarkably.

The thickness of the air chamber 102 formed in the back of the soundabsorbing body 103 is determined taking into account thesound-absorption frequency characteristic. For example, the thickness ispreferably in a range of from about 20 to about 100 mm.

The width and height of the ribs 106 formed on the sound absorbing body103, and the volume of the resonant spaces 105 may be determined takinginto account the sound-absorption frequency characteristic of acombination of the air chamber 102 and the through-holes 108. Forexample, the width of the widest portion of the ribs 106 is preferablyin a range of from about 40 to about 100 mm, and the height ispreferably in a range of from about 50 to about 100 mm. The width of theplurality of ribs 106 provided on the sound absorbing body 103 may beselected to be constant or different. For example, two kinds of ribs 106different in width may be disposed alternately. Because the width andheight of the ribs 106 has influence on the sound-absorption frequency,an effect of high sound absorption in different frequency bands isobtained by using ribs different in width and height.

The through-holes 108 are provided to make entrance of sound into theair chamber 102 easy. The numerical aperture, hole diameter, pitch, etc.thereof may be determined taking into account the sound-absorptionfrequency characteristic of a combination of the air chamber 102 and theresonant spaces 105. Generally, the numerical aperture is preferably ina range of from about 0.2 to about 10%. Further, the hole diameter ispreferably in a range of from about 3 to about 15 mm. Incidentally, thehole pitch may be determined correspondingly to the aforementionednumerical aperture and hole diameter ranges.

The sound absorbing body 103 is disposed as a front surface of the soundabsorbing structure, so that the rib 106 side surface is the surface ofthe sound absorbing structure. That is, the front surface of the soundabsorbing structure is in a state in which the plurality of ribs 106 aredisposed, so that the through-holes 108 formed in the basal portions 107are little visible. Accordingly, there is no flicker caused by thethrough-holes 108 though the sound absorbing structure has such a largenumber of through-holes 108, so that a stripe-like good externalappearance is obtained by arrangement of the ribs 106. Accordingly,there is no unpleasant feeling given to a person seeing the soundabsorbing structure, so that a good impression can be given.

Further, because the plurality of ribs 106 have a reinforcing effect,the strength of this sound absorbing structure is higher than that of asimply flat-plate-like porous board. Accordingly, the intervals betweensupport members such as spacers 104 for attaching the sound absorbingbody 103 to the wall 101 can be widened, so that the structure of thesound absorbing body 103 can be simplified. Furthermore, because thethrough-holes 108 are located in the deep positions of the grooves 109,stain or dust can be prevented from being deposited into thethrough-holes 108, so that the through-holes 108 can be prevented frombeing choked for a long term.

Although the aforementioned embodiment has shown the case wherethrough-holes 108 are formed in the center of the basal portions 107between the ribs 106, the positions in which the through-holes 108 areformed are not limited thereto and various changes may be made suitably.That is, the through-holes 108 may be disposed in any other positions ifthe through-holes 108 can be communicated with the inside air chamber102 or with the resonant spaces 105 and are little visible from theoutside. For example, the through-holes 108 may be formed in cornerportions of the basal portions 107 as shown in FIG. 17(a) or may beformed in side surfaces of the ribs 106 adjacent to the basal portions107 as shown in FIG. 17(b).

As described above, the ribs 106 are provided in order to form resonantspaces 105 to improve the sound absorbing property and make thethrough-holes 108 invisible. The sectional shape of the ribs 106 can bechanged variously and may be suitably designed taking into accountdesign.

In the embodiment of FIG. 15, the ribs 106 are shaped rectangularly soas to be widened toward the front end side. Accordingly, the grooves 109between the ribs 106 are narrowed toward the front end side, so thatthere arises an advantage that the effect of concealing thethrough-holes 108 in the basal portions 107 is high.

Examples shown in FIGS. 18(a) to 18(g) can be exemplified as othershapes.

In these drawings, the air chamber is located in the lower side, so thatthe outer surface (the front surface of the sound absorbing structure)is located in the upper side. In each of sound absorbing bodies 103,each of the ribs 106 has a portion with its sectional shape widenedtoward the front end side. Accordingly, the effect of concealing thethrough-holes (not shown in FIG. 18) formed in the basal portions 107 orrib 106 side surfaces is high, so that not only the external appearanceis made good but also stain or dust is prevented from being depositedinto the through-holes.

Alternatively, ribs 106 of a simple sectional shape as shown in FIGS.19(a) and 19(b) may be used. In this case, there arises an advantagethat the sound absorbing body 103 is produced easily.

The sound absorbing body 103 in the embodiment shown in FIG. 16 issimply constituted by a plurality of ribs 106 and basal portions 107between the ribs 106, and the sound absorbing body 103 is attached tothe wall surface 101 through the spacers 104. The sound absorbing body103 according to the present invention is, however, not limited to theaforementioned configuration, and the spacer 104 as mount legs forattachment to the wall surface may be integrated with the soundabsorbing body 103.

FIG. 20 shows a sound absorbing body 103A in this case. The soundabsorbing body 103A has a plurality of ribs 106, basal portions 107between the ribs 106, and legs 111 at opposite ends to thus form aone-board structure. The sound absorbing body 103A is attached to thewall surface 101 with use of the legs 111 so that an air chamber 102having a predetermined thickness can be formed between the soundabsorbing body 103A and the wall surface 101.

FIG. 21 shows a sound absorbing unit 113 obtained by using the soundabsorbing body 103 and the air chamber 102 as one unit.

That is, the sound absorbing unit 113 is formed as a united structurefrom a sound absorbing body 103 disposed in the front and a back board114 disposed in the back with separation to form an air chamber 102. Thesound absorbing unit 113 has an advantage that a sound absorbing wallhaving a constant sound absorbing property can be formed easily only byarranging sound absorbing units 113 side by side. Any one of theaforementioned materials can be used suitably as the sound absorbingbody 103.

Although the aforementioned embodiment has shown the case where the airchamber 102 in the back of the sound absorbing body 103 forms one largespace, the air chamber 102 may be partitioned into a plurality of smallchambers.

FIG. 22 shows embodiments in which the air chamber 102 is partitionedinto small chambers.

In the sound absorbing unit 113A shown in FIG. 22(a), two kinds of ribs106a and 106b different in width are alternately disposed on the soundabsorbing body 103 disposed in the front so that grooves 109a and 109bdifferent in width are formed between the ribs 106a and 106b. Further,partition walls 115 are provided on the rear surfaces of one endportions of the basal portions 107, that is, on the extension lines ofone-side surfaces of the ribs 106a and 106b, so that the air chamber ispartitioned into a plurality of small chambers 102a and 102b.

In such configuration, the air chamber is partitioned into air chambers102a and 102b different in volume, so that one air chamber 102a absorbsa sound of a certain frequency whereas the other air chamber 102babsorbs a sound of a different frequency. Accordingly, there arises anadvantage that the sound-absorption frequency band is widened.

Further, in the sound absorbing unit 113B shown in FIG. 22(b), partitionwalls 115 are provided in the ribs 106a and 106b. Also in this case, thesame effect as shown in FIG. 22(a) is obtained.

Although the embodiments shown in FIGS. 22(a) and 22(b) has beendescribed upon the case where the air chamber is partitioned into airchambers different in volume, the air chamber may be partitioned intoequal volume air chambers. When the air chamber is partitioned intosmall-volume chambers, the sound absorbing property is improved withrespect to a sound in a narrow frequency band corresponding to thevolume of the air chambers obtained by partition. Accordingly, partitionis effective in the case where the frequency of noise produced islimited to a narrow frequency range.

Although the sound absorbing units 113A and 113B of FIGS. 22(a) and22(b), have been described upon the case where the ribs 106a and 106b ofthe sound absorbing body 103 in the front are shaped simplyrectangularly, the shape of the sound absorbing body 103 in the front isnot limited thereto and various shapes may be used as shown in FIGS. 15to 19.

That is, partition walls 115 shown in FIG. 22 may be provided in theback of the sound absorbing body 103 shown in FIGS. 15 to 19 so that theair chamber is partitioned into a plurality of air chambers. Further, itis unnecessary that the back board 114 is always provided when suchpartition walls 115 are provided. For example, when the sound absorbingbody 103 is attached to the wall surface 101 (see FIG. 15), thepartition walls 115 may strike on the wall surface 101 so that the airchamber between the sound absorbing body 103 and the wall surface 101can be partitioned into a plurality of air chambers.

Although the above embodiment has shown the case where the soundabsorbing body 103 is made from a board material and constituted by ribs106 and basal portions 107, a combination of sound absorbing materialsand the sound absorbing body 103 may be used.

FIGS. 23(a), 23(b), and 23(c) show examples in which the sound absorbingbody 103 is combined with the sound absorbing material.

FIG. 23(a) shows the case where a board-like sound absorbing material117 is disposed on the air chamber side surface, that is, back surfaceof the sound absorbing body 103, FIG. 23(b) shows the case where soundabsorbing materials 118 are disposed on the outer surfaces of the basalportions 107 between the ribs 106 of the sound absorbing body 103, andFIG. 23(c) shows the case where cylindrical sound absorbing materials119 are disposed in the grooves 109 formed between the ribs 106. Each ofthe sound absorbing materials 117, 118 and 119 used herein is a materialhaving a sound absorbing effect in itself. Generally, porous materialssuch as glass wool, rock wool, fiber mat material, etc., film materialssuch as sail cloth, etc., and so on, are used. When such sound absorbingmaterials are used in combination, the sound-absorption frequency bandcan be widened.

Results of measurement of the sound absorbing property of various soundabsorbing bodies according to embodiments of the present invention willbe described below.

EXAMPLES 5 to 12!

The sound absorbing structures used are as shown in the diagrams ofFIGS. 24(a) to 24(h) which correspond to examples 5 to 12, respectively.The unit of size shown in the diagrams is mm.

The sound absorbing body 103 of the diagram (6) was produced by addingthe sound absorbing material 117 to the sound absorbing body 103 of thediagram (5). The sound absorbing body 103 of the diagram (3) or (4) wasproduced by changing the thickness of the air chamber in the back of thesound absorbing body 103 of the diagram (5) and adding the soundabsorbing materials 117 and 118 to the sound absorbing body 103 of thediagram (5). In the sound absorbing body 103 shown in the diagrams (5)to (8), one row of through-holes 108 with a diameter of 9 mm weredisposed in the center of the basal portion 107 at intervals of a pitchof 50 mm. The sound absorbing body 3 of the diagram (10) was produced byadding the sound absorbing materials 118 to the sound absorbing body 103of the diagram (9). In the sound absorbing body 103 shown in thediagrams (9) and (10), one row of through-holes 108 with a diameter of10 mm were disposed in the center of the basal portion 107 at intervalsof a pitch of 100 mm. The sound absorbing body 103 of the diagram (12)was produced by adding the sound absorbing materials 118 to the soundabsorbing body 103 of the diagram (11). In the sound absorbing body 103shown in the diagrams (11) and (12), one row of through-holes 108 with adiameter of 9 mm were formed in the center of the basal portion 107 inthe bottom surface of a narrower groove 109a at intervals of a pitch of50 mm, and one row of through-holes 108 with a diameter of 10 mm wereformed in the center of the basal portion 107 in the bottom surface of awider groove 109b at intervals of a pitch of 100 mm. The sound absorbingmaterials 117 and 118 used were glass wool.

The sound absorbing rate of each sound absorbing structure shown in FIG.24 was measured to obtain a statistical incidence sound absorbing rate.Results thereof are shown in Table 3. Incidentally, the unit of thestatistical incidence sound absorbing rate shown in Table 3 is %.

                  TABLE 3                                                         ______________________________________                                        Frequency (Hz)                                                                63       80     100    125  160  200  250  315  400                           ______________________________________                                        Ex.                                                                            5     9     13     12   17   28   53   81   82   53                           6    15     24     28   44   63   85   83   84   82                           7    20     28     40   66   82   86   77   60   44                           8    32     43     61   77   86   84   86   80   82                           9    22     39     48   86   84   59   42   34   30                          10    47     74     83   86   81   70   60   53   50                          11    20     54     76   39   85   53   32   60   22                          12    59     80     74   83   77   66   65   65   43                          Co. Ex.                                                                        4    --     --     --   35   42   35   37   30   27                           5    --     --     --   68   80   86   82   72   67                           6    --     --     --   62   77   92   94   90   92                          ______________________________________                                    

Comparative Examples 4 to 6!

As shown in FIGS. 25(a) to 25(c), in the case (Comparative Example 4) aporous gypsum board 120 was disposed to form a 300 mm air chamber 102 infront of the wall surface 101, in the case (Comparative Example 5) wherea rock wool sound absorbing felt 122 with a thickness of 25 mm wasdisposed in the back surface of the porous gypsum board 120, and in thecase (Comparative Example 6) where a porous calcium silicate board 123was disposed to form a 300 mm air chamber 102 in front of the wallsurface 101 and a rock wool sound absorbing felt 122 with a thickness of25 mm is disposed in the back of the porous calcium silicate board 123,the results of sound absorption are also shown in Table 3.

Results of Table 3 are shown as graphs of FIGS. 26 to 28. Referencenumerals (5) to (12) in the drawings correspond to examples 5 to 12,respectively.

It is apparent from Table 3 and FIGS. 26 through 28 that in Examples 5and 9, there is a region exhibiting a high sound absorbing rate in arelatively narrow frequency band and that particularly in Example 9,there is a peak of the sound absorbing rate in a low frequency band offrom 125 to 160 Hz. Accordingly, a sound absorbing structure having ahigh sound absorbing rate in a desired low frequency band can beachieved by designing the width of the ribs 106 and the depth of the airchamber 102 suitably.

Further, in Example 11, there are peaks of high sound absorbing rate ina plurality of frequency bands. Accordingly, the Example 11 is adaptedfor the purpose of requiring sound absorption in a plurality offrequency bands.

Further, in comparison between the case where the sound absorbingmaterial 117 or 118 is used (Examples 6, 7, 8, 9, 12) and the case wherethe sound absorbing material is not used, the sound absorbing rate inthe wide frequency band is improved, though the peak sound absorbingrate is not so changed. Accordingly, when the frequency band of noise iswide, the sound absorbing material is preferably used.

Further, in comparison between results of Examples 7 and 8, the soundabsorbing property in Example 8 is superior. Accordingly, the soundabsorbing material 118 is preferably disposed on the outer surface ofthe sound absorbing body 103 if only the sound absorbing property istaken into account.

On the contrary, the sound absorbing effect in Comparative Example 4 islow as a whole, so that it cannot be said that Comparative Example 4 iseffective. In Comparative Examples 5 and 6, the sound absorbing effectis improved considerably but the effect is mainly obtained in afrequency band of not lower than 200 Hz. There is no improvement of theeffect in a low frequency band of not higher than 160 Hz.

On the contrary, in Examples 7 to 12 of the present invention, not onlya considerable sound absorbing effect is obtained in a low frequencyband of not higher than 160 Hz but also a sufficient sound absorbingeffect is obtained even in the case where the thickness of the soundabsorbing structure as a whole is reduced to 150 mm which is a half thethickness 300 mm in Comparative Examples 4 to 6. It is thought that thiseffect is obtained by the resonant spaces 105 formed in the ribs 106.

(Effects of the Invention)

As described above, in the sound absorbing body according to the presentinvention, a plurality of ribs each having a desired cross-sectionalshape are formed convexly at predetermined intervals on a front surfaceof the sound absorbing body for reinforcing the sound absorbing body.Further, through-holes are formed through the sound absorbing body fromits front surface to its back surface correspondingly to the respectiveribs. Furthermore, concealing materials are provided between the ribs onthe front surface of the sound absorbing body for concealing thethrough-holes. Accordingly, for example, when the sound absorbing bodyis attached in the front of an air chamber so that the surface on whichthe ribs are formed is located in the outside, a sound absorbingstructure good in sound absorbing property particularly in a lowfrequency band can be formed, and there can be obtained a goodappearance in which no flicker is caused by the through-holes, and theplurality of ribs are arranged. Further, more superior appearances canbe provided by suitably modifying the sectional shapes or the like ofthe ribs so that the design can be changed variously. Further, dust canbe prevented from adhering on the inside surface of the through-holesand blockage of the through-holes or the like can be prevented for along term. In addition, the strength of the sound absorbing board can beincreased by the reinforcing effect of the ribs.

According to the sound absorbing body of an embodiment of the presentinvention, in the sound absorbing body, the ribs are provided integrallywith the sound absorbing body, so that the number of assembling stepscan be decreased and the strength of the sound absorbing body can beincreased.

According to the sound absorbing body of the invention, a plurality ofribs each having a predetermined sectional shape are protruded from atleast one of the surfaces of the sound absorbing main body, withpredetermined intervals therebetween. Further, a plurality ofthrough-holes are formed correspondingly to the respective ribs so as topass through the sound absorbing main body from one side thereof to theother side. Accordingly, for example, when the sound absorbing body isattached in the front of an air chamber so that the surface on which theribs are formed is located in the outside, a sound absorbing structuregood in sound absorbing property particularly in a low frequency bandcan be formed, and there can be obtained a good appearance in which noflicker is caused by the through-holes, and the plurality of ribs arearranged. Further, more superior appearances can be provided by suitablymodifying the sectional shapes or the like of the ribs so that thedesign can be changed variously. Further, since the ribs are providedintegrally with the sound absorbing main body, the number of assemblingsteps can be reduced and the strength of the sound absorbing body can beincreased.

According to the sound absorbing board of another embodiment of thepresent invention, a plurality of ribs provided on a front surface ofthe sound absorbing board body for reinforcing the sound absorbing bodyand a plurality of through-holes formed in the base portions between theribs on the front surface of the sound absorbing body are provided.Accordingly, when the sound absorbing board body is attached in thefront of an air chamber so that the surface on which the ribs are formedis located in the outside, a sound absorbing structure good in soundabsorbing property particularly in a low frequency band can be formed.Further, an external appearance in which the large number of ribs aredisposed is obtained so that there is no flicker caused by the holes andno unpleasant feeling given to a person even though the large number ofholes are formed. Further, various external appearances can be providedby appropriately changing the intervals between the ribs and the widthof the ribs, so that the design can be changed variously. Further, theplurality of ribs also have a reinforcing function, so that the strengthof the sound absorbing board can be improved. Further, since theconcealing materials for concealing the through-holes are provided onthe front surface of the sound absorbing board body, the through-holesare not seen from the outside so that no further visual flickering orthe like is caused by a number of through-holes and a good appearancecan be obtained. Further, dust can be prevented from adhering on theinside surface of the through-holes and blockage of the through-holes orthe like can be prevented for a long term. In addition, the strength, ofthe sound absorbing board can be increased by the reinforcing effect ofthe ribs.

According to the sound absorbing board according to another aspect ofthe present invention, a plurality of ribs each having a cross-sectionalshape widened toward its top end are provided on a front surface of thesound absorbing board body, and the sound absorbing board body has aporous structure in which a plurality of through-holes are formedthrough the sound absorbing board body to reach its back surface inportions at root ends of the ribs concealed by the top ends of the ribs.Accordingly, for example, by attaching the sound absorbing board in thefront of the air chamber such that the side on which the ribs are formedis made outside, it is possible to constitute a sound absorbingstructure which is superior in sound absorbing characteristic especiallyin the low frequency area. The appearance shows a shape in which numbersof ribs are disposed side-by-side, and a number of through-holes areformed in positions concealed by the ribs. Further, each rib is made tohave a cross-sectional shape widened toward its top end like a reversedtrapezoid and the diameter of each through-hole is set to be longer thanthe width of the root end of the rib and shorter than the width of thetop end of the rib so that the through-holes open on both sides of eachof the ribs. Accordingly, in spite of the fact that each through-holecan be set to have a relatively large aperture diameter, thethrough-holes, are not so clearly seen from the outside, so that it ispossible to obtain a preferable appearance having no visual flickeringor the like caused by the numbers of through-holes. In addition, thestrength of the sound absorbing board can be increased by thereinforcing effect of the ribs.

According to a sound absorbing body of the invention, a plurality ofribs are provided to project to a side opposite to the air chamber so asto form resonant spaces communicated with the air chamber; and aplurality of through-holes are formed at least in the ribs or in thebasal portions formed between the ribs so as to communicate with the airchamber. Accordingly, there can be obtained a sound absorbing structuregood in sound absorbing property particularly in a low frequency band bya combination of the sound absorbing body and the air chamber.Furthermore, because spaces in the ribs serve as resonant spaces in thisoccasion, not only the sound absorbing property is improved but also thesound absorbing structure can be made thin compared with the case wherethe conventional porous board is used. For example, the thickness of thesound absorbing structure can be reduced to 150 mm, which is a half thethickness 300 mm in the case where the porous board is used, whilekeeping the sound absorbing effect.

Furthermore, with respect to the external appearance, the plurality ofribs are disposed in the front, so that the through-holes areinconspicuous. Accordingly, there is no flicker caused by thethrough-holes, so that no unpleasant feeling is given. Furthermore,various external appearances can be provided by changing the intervaland width of the ribs suitably, so that the design can be changedvariously. Further, the strength of the sound absorbing body can beimproved by the reinforcing effect of the ribs.

According to a sound absorbing body of the invention, the soundabsorbing body comprises a sound absorbing material which is disposed atleast on inner or outer surface of the basal portions between the ribs,by which not only the resonant frequency band can be widened but alsothe sound absorbing property in a wide frequency band can be improved.

According to a sound absorbing body of the invention, the soundabsorbing body comprises partition walls which are disposed at least onthe rear surfaces of the ribs or on the basal portions between the ribsto partition the spaces in the air chamber located in the back.Accordingly, a plurality of independent small chambers are formed sothat resonant frequencies corresponding to the independent smallchambers can be provided, or in other words, a sound absorbing structurehaving a desired sound absorbing property can be designed easily if thevolumes of the independent small chambers are designed to be in valuescorresponding to required resonant frequencies.

According to a sound absorbing body of the invention, each of the ribshas a portion with its sectional shape widened toward the front end.Accordingly, the effect in which the ribs conceal the through-holes ishigh, so that a good external appearance is obtained. At the same time,there arises an effect that stain or dust is prevented from beingdeposited into the through-holes, so that the through-holes can beprevented from being choked for a long term.

According to a sound absorbing body of the invention, the volumes ofresonant spaces formed by the ribs are classified into two or morekinds. Accordingly, a plurality of resonant frequencies can be provided,so that the sound absorbing property in a wide frequency band can beimproved. If a sound absorbing material is used in addition to the soundabsorbing body of such a structure, sound absorbing characteristic inthe wider frequency range can be improved so that noises of a widefrequency range can be effectively absorbed.

Accordingly to a sound absorbing unit of the invention, the soundabsorbing unit comprises the sound absorbing body as mentioned above;and a back board integrally provided with the sound absorbing body anddisposed in the back of the sound absorbing body at a distance so as todefine an air chamber therebetween. Accordingly, a wall surface having arequired sound absorbing property can be formed simply by arranging suchsound absorbing units, so that a sound absorbing structure can beproduced easily on site. In the sound absorbing body according toembodiments of the present invention, the configuration is such that theribs and the concealing materials are made even in their upper surfaceor the upper surface of the ribs project beyond the upper surface or theupper surface of the ribs project beyond the upper surface of theconcealing materials because the height of the upper surface of theconcealing materials is made to be not higher than the upper surface ofthe ribs. Accordingly, it is possible top prevent the concealingmaterials from being injured by being caught by something.

What is claimed is:
 1. A sound absorbing body comprising:a soundabsorbing main body formed substantially in the shape of a plate; aplurality of projecting ribs at predetermined intervals on a frontsurface side of said sound absorbing main body for reinforcing saidsound absorbing main body, each of said ribs having a desiredcross-sectional shape; through-holes formed through said sound absorbingmain body from a front surface thereof to to a back surface thereof atrespective locations positioned between said ribs; and concealingmaterials disposed between said ribs on the front surface side of saidsound absorbing main body and concealing said through-holes; whereinslits are formed between the concealing materials and said ribs whichcommunicate with said through-holes.
 2. A sound absorbing body asclaimed in claim 1, wherein the ribs are provided integrally with thesound absorbing main body.
 3. A sound absorbing board comprising:a soundabsorbing board body formed into a substantially flat plate; a pluralityof ribs provided on a front surface of said sound absorbing board bodyfor reinforcing said sound absorbing board body; a plurality ofthrough-holes disposed at a base portion between said ribs provided insaid sound absorbing board body; and concealing materials disposed onthe front surface of said sound absorbing board body and concealing saidthrough-holes; wherein slits are formed between the concealing materialsand said ribs which communicate with said through-holes.
 4. A soundabsorbing board as claimed in claim 3, wherein the height of an uppersurface of said concealing materials is not higher than the height of anupper surface of said ribs.
 5. A sound absorbing body as claimed inclaim 1, wherein the height of an upper surface of said concealingmaterials is not higher than the height of an upper surface of saidribs.
 6. A sound absorbing body as claimed in claim 1, wherein each ofthe concealing materials has a width which is larger than a diameter ofthe through-holes concealed thereby.
 7. A sound absorbing body asclaimed in claim 3, wherein each of the concealing materials has a widthwhich is larger than a diameter of the through-holes concealed thereby.8. A sound absorbing body as claimed in claim 3, wherein said slits havea sectional area between the ribs and concealing materials which islarger than a cross-sectional area of the through-holes.
 9. A soundabsorbing body as claimed in claim 1, wherein said slits have asectional area between the ribs and concealing materials which is largerthan a cross-sectional area of the through-holes.